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-rw-r--r--contrib/Makefile1
-rw-r--r--contrib/old_snapshot/Makefile22
-rw-r--r--contrib/old_snapshot/old_snapshot--1.0.sql14
-rw-r--r--contrib/old_snapshot/old_snapshot.control5
-rw-r--r--contrib/old_snapshot/time_mapping.c159
-rw-r--r--doc/src/sgml/contrib.sgml1
-rw-r--r--doc/src/sgml/filelist.sgml1
-rw-r--r--doc/src/sgml/oldsnapshot.sgml33
8 files changed, 236 insertions, 0 deletions
diff --git a/contrib/Makefile b/contrib/Makefile
index c8d2a162735..7a4866e338d 100644
--- a/contrib/Makefile
+++ b/contrib/Makefile
@@ -27,6 +27,7 @@ SUBDIRS = \
lo \
ltree \
oid2name \
+ old_snapshot \
pageinspect \
passwordcheck \
pg_buffercache \
diff --git a/contrib/old_snapshot/Makefile b/contrib/old_snapshot/Makefile
new file mode 100644
index 00000000000..77c85df3225
--- /dev/null
+++ b/contrib/old_snapshot/Makefile
@@ -0,0 +1,22 @@
+# contrib/old_snapshot/Makefile
+
+MODULE_big = old_snapshot
+OBJS = \
+ $(WIN32RES) \
+ time_mapping.o
+PG_CPPFLAGS = -I$(libpq_srcdir)
+
+EXTENSION = old_snapshot
+DATA = old_snapshot--1.0.sql
+PGFILEDESC = "old_snapshot - utilities in support of old_snapshot_threshold"
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = contrib/old_snapshot
+top_builddir = ../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif
diff --git a/contrib/old_snapshot/old_snapshot--1.0.sql b/contrib/old_snapshot/old_snapshot--1.0.sql
new file mode 100644
index 00000000000..9ebb8829e37
--- /dev/null
+++ b/contrib/old_snapshot/old_snapshot--1.0.sql
@@ -0,0 +1,14 @@
+/* contrib/old_snapshot/old_snapshot--1.0.sql */
+
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION old_snapshot" to load this file. \quit
+
+-- Show visibility map and page-level visibility information for each block.
+CREATE FUNCTION pg_old_snapshot_time_mapping(array_offset OUT int4,
+ end_timestamp OUT timestamptz,
+ newest_xmin OUT xid)
+RETURNS SETOF record
+AS 'MODULE_PATHNAME', 'pg_old_snapshot_time_mapping'
+LANGUAGE C STRICT;
+
+-- XXX. Do we want REVOKE commands here?
diff --git a/contrib/old_snapshot/old_snapshot.control b/contrib/old_snapshot/old_snapshot.control
new file mode 100644
index 00000000000..491eec536cd
--- /dev/null
+++ b/contrib/old_snapshot/old_snapshot.control
@@ -0,0 +1,5 @@
+# old_snapshot extension
+comment = 'utilities in support of old_snapshot_threshold'
+default_version = '1.0'
+module_pathname = '$libdir/old_snapshot'
+relocatable = true
diff --git a/contrib/old_snapshot/time_mapping.c b/contrib/old_snapshot/time_mapping.c
new file mode 100644
index 00000000000..37e0055a008
--- /dev/null
+++ b/contrib/old_snapshot/time_mapping.c
@@ -0,0 +1,159 @@
+/*-------------------------------------------------------------------------
+ *
+ * time_mapping.c
+ * time to XID mapping information
+ *
+ * Copyright (c) 2020, PostgreSQL Global Development Group
+ *
+ * contrib/old_snapshot/time_mapping.c
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "funcapi.h"
+#include "storage/lwlock.h"
+#include "utils/old_snapshot.h"
+#include "utils/snapmgr.h"
+#include "utils/timestamp.h"
+
+/*
+ * Backend-private copy of the information from oldSnapshotControl which relates
+ * to the time to XID mapping, plus an index so that we can iterate.
+ *
+ * Note that the length of the xid_by_minute array is given by
+ * OLD_SNAPSHOT_TIME_MAP_ENTRIES (which is not a compile-time constant).
+ */
+typedef struct
+{
+ int current_index;
+ int head_offset;
+ TimestampTz head_timestamp;
+ int count_used;
+ TransactionId xid_by_minute[FLEXIBLE_ARRAY_MEMBER];
+} OldSnapshotTimeMapping;
+
+#define NUM_TIME_MAPPING_COLUMNS 3
+
+PG_MODULE_MAGIC;
+PG_FUNCTION_INFO_V1(pg_old_snapshot_time_mapping);
+
+static OldSnapshotTimeMapping *GetOldSnapshotTimeMapping(void);
+static TupleDesc MakeOldSnapshotTimeMappingTupleDesc(void);
+static HeapTuple MakeOldSnapshotTimeMappingTuple(TupleDesc tupdesc,
+ OldSnapshotTimeMapping *mapping);
+
+/*
+ * SQL-callable set-returning function.
+ */
+Datum
+pg_old_snapshot_time_mapping(PG_FUNCTION_ARGS)
+{
+ FuncCallContext *funcctx;
+ OldSnapshotTimeMapping *mapping;
+
+ if (SRF_IS_FIRSTCALL())
+ {
+ MemoryContext oldcontext;
+
+ funcctx = SRF_FIRSTCALL_INIT();
+ oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
+ mapping = GetOldSnapshotTimeMapping();
+ funcctx->user_fctx = mapping;
+ funcctx->tuple_desc = MakeOldSnapshotTimeMappingTupleDesc();
+ MemoryContextSwitchTo(oldcontext);
+ }
+
+ funcctx = SRF_PERCALL_SETUP();
+ mapping = (OldSnapshotTimeMapping *) funcctx->user_fctx;
+
+ while (mapping->current_index < mapping->count_used)
+ {
+ HeapTuple tuple;
+
+ tuple = MakeOldSnapshotTimeMappingTuple(funcctx->tuple_desc, mapping);
+ ++mapping->current_index;
+ SRF_RETURN_NEXT(funcctx, HeapTupleGetDatum(tuple));
+ }
+
+ SRF_RETURN_DONE(funcctx);
+}
+
+/*
+ * Get the old snapshot time mapping data from shared memory.
+ */
+static OldSnapshotTimeMapping *
+GetOldSnapshotTimeMapping(void)
+{
+ OldSnapshotTimeMapping *mapping;
+
+ mapping = palloc(offsetof(OldSnapshotTimeMapping, xid_by_minute)
+ + sizeof(TransactionId) * OLD_SNAPSHOT_TIME_MAP_ENTRIES);
+ mapping->current_index = 0;
+
+ LWLockAcquire(OldSnapshotTimeMapLock, LW_SHARED);
+ mapping->head_offset = oldSnapshotControl->head_offset;
+ mapping->head_timestamp = oldSnapshotControl->head_timestamp;
+ mapping->count_used = oldSnapshotControl->count_used;
+ for (int i = 0; i < OLD_SNAPSHOT_TIME_MAP_ENTRIES; ++i)
+ mapping->xid_by_minute[i] = oldSnapshotControl->xid_by_minute[i];
+ LWLockRelease(OldSnapshotTimeMapLock);
+
+ return mapping;
+}
+
+/*
+ * Build a tuple descriptor for the pg_old_snapshot_time_mapping() SRF.
+ */
+static TupleDesc
+MakeOldSnapshotTimeMappingTupleDesc(void)
+{
+ TupleDesc tupdesc;
+
+ tupdesc = CreateTemplateTupleDesc(NUM_TIME_MAPPING_COLUMNS);
+
+ TupleDescInitEntry(tupdesc, (AttrNumber) 1, "array_offset",
+ INT4OID, -1, 0);
+ TupleDescInitEntry(tupdesc, (AttrNumber) 2, "end_timestamp",
+ TIMESTAMPTZOID, -1, 0);
+ TupleDescInitEntry(tupdesc, (AttrNumber) 3, "newest_xmin",
+ XIDOID, -1, 0);
+
+ return BlessTupleDesc(tupdesc);
+}
+
+/*
+ * Convert one entry from the old snapshot time mapping to a HeapTuple.
+ */
+static HeapTuple
+MakeOldSnapshotTimeMappingTuple(TupleDesc tupdesc, OldSnapshotTimeMapping *mapping)
+{
+ Datum values[NUM_TIME_MAPPING_COLUMNS];
+ bool nulls[NUM_TIME_MAPPING_COLUMNS];
+ int array_position;
+ TimestampTz timestamp;
+
+ /*
+ * Figure out the array position corresponding to the current index.
+ *
+ * Index 0 means the oldest entry in the mapping, which is stored at
+ * mapping->head_offset. Index 1 means the next-oldest entry, which is a the
+ * following index, and so on. We wrap around when we reach the end of the array.
+ */
+ array_position = (mapping->head_offset + mapping->current_index)
+ % OLD_SNAPSHOT_TIME_MAP_ENTRIES;
+
+ /*
+ * No explicit timestamp is stored for any entry other than the oldest one,
+ * but each entry corresponds to 1-minute period, so we can just add.
+ */
+ timestamp = TimestampTzPlusMilliseconds(mapping->head_timestamp,
+ mapping->current_index * 60000);
+
+ /* Initialize nulls and values arrays. */
+ memset(nulls, 0, sizeof(nulls));
+ values[0] = Int32GetDatum(array_position);
+ values[1] = TimestampTzGetDatum(timestamp);
+ values[2] = TransactionIdGetDatum(mapping->xid_by_minute[array_position]);
+
+ return heap_form_tuple(tupdesc, values, nulls);
+}
diff --git a/doc/src/sgml/contrib.sgml b/doc/src/sgml/contrib.sgml
index c82dde27263..4e833d79ef9 100644
--- a/doc/src/sgml/contrib.sgml
+++ b/doc/src/sgml/contrib.sgml
@@ -116,6 +116,7 @@ CREATE EXTENSION <replaceable>module_name</replaceable>;
&isn;
&lo;
&ltree;
+ &oldsnapshot;
&pageinspect;
&passwordcheck;
&pgbuffercache;
diff --git a/doc/src/sgml/filelist.sgml b/doc/src/sgml/filelist.sgml
index 828396d4a9e..47271addc14 100644
--- a/doc/src/sgml/filelist.sgml
+++ b/doc/src/sgml/filelist.sgml
@@ -129,6 +129,7 @@
<!ENTITY lo SYSTEM "lo.sgml">
<!ENTITY ltree SYSTEM "ltree.sgml">
<!ENTITY oid2name SYSTEM "oid2name.sgml">
+<!ENTITY oldsnapshot SYSTEM "oldsnapshot.sgml">
<!ENTITY pageinspect SYSTEM "pageinspect.sgml">
<!ENTITY passwordcheck SYSTEM "passwordcheck.sgml">
<!ENTITY pgbuffercache SYSTEM "pgbuffercache.sgml">
diff --git a/doc/src/sgml/oldsnapshot.sgml b/doc/src/sgml/oldsnapshot.sgml
new file mode 100644
index 00000000000..a665ae72e78
--- /dev/null
+++ b/doc/src/sgml/oldsnapshot.sgml
@@ -0,0 +1,33 @@
+<!-- doc/src/sgml/oldsnapshot.sgml -->
+
+<sect1 id="oldsnapshot" xreflabel="old_snapshot">
+ <title>old_snapshot</title>
+
+ <indexterm zone="oldsnapshot">
+ <primary>old_snapshot</primary>
+ </indexterm>
+
+ <para>
+ The <filename>old_snapshot</filename> module allows inspection
+ of the server state that is used to implement
+ <xref linkend="guc-old-snapshot-threshold" />.
+ </para>
+
+ <sect2>
+ <title>Functions</title>
+
+ <variablelist>
+ <varlistentry>
+ <term><function>pg_old_snapshot_time_mapping(array_offset OUT int4, end_timestamp OUT timestamptz, newest_xmin OUT xid) returns setof record</function></term>
+ <listitem>
+ <para>
+ Returns all of the entries in the server's timestamp to XID mapping.
+ Each entry represents the newest xmin of any snapshot taken in the
+ corresponding minute.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </sect2>
+
+</sect1>
generated by cgit v1.2.3 (git 2.25.1) at 2025-05-30 21:49:01 +0000